A Concurrent CSMA MAC protocol for Mobile Ad Hoc Networks using beamnulling

Traditional algorithms for Media Access Control (MAC) in Mobile Ad Hoc Networks (MANET) such as CSMA-CA allow only a single user to transmit at a given time. This means that the sum throughput in a MANET cannot increase to service additional users. Such MAC protocols disregard the possibility that by utilizing multiple antenna processing to handle interference intelligently at the Physical layer (PHY), many concurrent user transmissions can co-exist. Previous works have proposed altered versions of CSMA-CA that allow multi user operation but may not necessarily be able to coexist with an existing IEEE 802.11 based network. This paper proposes a Concurrent CSMA MAC protocol that is completely compatible with traditional CSMA based MAC and follows the same timing structure allowing co-existence of both protocols. Specifically, in Concurrent CSMA after a primary user has captured the channel, secondary users listen to the RTS/CTS handshake and form a beamnull towards the primary receiver. Hence secondary users can communicate concurrently with minimal increase in interference to the primary receiver. Simulations show that the proposed PHY and MAC scheme is able to achieve 2 to 3 times the network spectral efficiency of CSMA with a single antenna and this improvement factor is sustained as the network scales in size. Further the proposed scheme allows the network spectral efficiency (sum throughput per unit bandwidth) to scale with users and improves upon a previous promising approach which uses Interference Alignment.